Solvent refining of naphthenic lube oil with n-methyl-2-pyrrolidone

ABSTRACT

MANUFACTURE OF NAPHTHENIC LUBRICATING OIL PRODUCT BY DISTILLATION OF CRUDE OIL CONTAINING NAPHTHENIC LUBRICATING OIL EFFECTING SEPARATION OF THE NAPHTHENIC LUBRICATING OIL STOCKS; REFINING LUBRICATING OIL STOCKS FOR REMOVAL OF CONSTITUENTS OF LOW VISCOSITY INDEX, LOW THERMAL STABILITY, AND POOR OXIDATION STABILITY BY SOLVENT EXTRACTION WITH AN AQUEOUS SOLVENT PHASE COMPRISING BETWEEN ABOUT 85 AND 98 WT. PERCENT N-METHYL-2-PYRROLIDONE AND BETWEEN ABOUT 2 AND 15 WT. PERCENT WATER AT CONDITIONS EFFECTIVE TO DISSOLVE AT LEAST 10 VOL. PERCENT PRODUCING AS A RAFFINATE A REFINED LUBRICATING STOCK OF SAID LUBRICATING OIL STOCKS OF IMPROVED VISCOSITY INDEX, THERMAL STABILITY AND OXIDATION STABILITY.

United States Patent 3,661,772 SOLVENT REFINING 0F NAPHTHENIC LUBE OIL WITH N-METHYL-Z-PYRROLIDONE Avilino Sequeira, Jr., and James P. Jolly, Nederland, Tex., and William E. Rea, Hopewell Junction, N.Y., assignors to Texaco Inc., New York, NY. No Drawing. Filed Apr. 3, 1970, Ser. No. 25,592 Int. Cl. Cg 29/00 U.S. Cl. 208-289 2 Claims ABSTRACT OF THE DISCLOSURE Manufacture of naphthenic lubricating oil product by distillation of crude oil containing naphthenic lubricating oil effecting separation of the naphthenic lubricating oil stocks; refining lubricating oil stocks for removal of constituents of low viscosity index, low thermal stability, and poor oxidation stability by solvent extraction with an aqueous solvent phase comprising between about 85 and 98 wt. percent N-methyl-Z-pyrrolidone and between about 2 and wt. percent water at conditions effective to dissolve at least 10 vol. percent producing as a raflinate a refined lubricating stock of said lubricating oil stocks of improved viscosity index, thermal stability and oxidation stability.

BACKGROUND OF THE INVENTION In the manufacture of naphthenic lubricating oil from crude petroleum one or more fractions containing the naphthenic lubricating oil constituents are separated by distillation, usually by vacuum distillation. The raw lubricating oil fractions contain unstable naturally occurring materials which tend to form deposits or become corrosive in operating equipment as a result of heating and oxidation or both. Additionally, it is often desirable to increase the viscosity index of the lubricating oil by removing the more aromatic lower viscosity index constituents from the oil. To accomplish this it is necessary to remove or destroy a significant amount of material present in the raw stock, typically ranging from 10 to 60 percent depending on the qualities desired in the product oil. The most common way to do this is by extraction with a solvent having selectivity for the more unstable molecules which are predominantly aromatic and nonhydrocarbon materials. Prior to the advent of solvent extraction, severe treatment with concentrated sulfuric acid was commonly used to destroy these undesirable materials.

In the treatment of oils to remove unstable, corrosive and low viscosity constituents of oil, a substantial amount of material is removed from the charge stock, that is, an amount in excess of about 10 volume percent. This is distinctly different from decolorizing treatment in lubricating oil manufacture where only trace amounts of coloring material are removed, typically less than 1.0 percent. Such color improvement steps are often used after solvent refining. A raw stock that is only treated for color improvement is usually unsatisfactory as regards thermal and oxidation stability or viscosity index.

This invention is particularly directed to the solvent extraction step in the manufacture of naphthenic lubricating oils by the sequence of distillation, solvent extraction, solvent dewaxing (optional) and blending. Broadly, the solvent extraction in the invention is accomplished with aqueous N-methyl-Z-pyrrolidone at a temperature of at least 50 F. and below the temperature of complete miscibility of the lubricating oil stock in N-methyl-Z-pyrrolidone and at a dosage efiective to dissolve at least 10 volume percent of said lubricating oil stock whereby a refined lubricating oil stock is produced of improved oxidation stability.

3,661,772 Patented May 9, 1972 Heretofore, anhydrous and essentially anhydrous, N- methyl-2-pyrrolidone has been known as a solvent for the separation of constituents of low thermal and oxidation stability from lubricating oil fractions and for the separation of low viscosity index constituents from lubricating oil. However, when naphthenic oil is the lubricating oil to be refined several unexpectedly undesirable factors arise in the refining process using anhydrous and essentially anhydrous N-methyl-Z-pyrrolidone. Specifically, in the case of naphthenic residual stocks there results high miscibility of the stock in the solvent and relatively high viscosity of the refining mixture, particularly when low solvent dosage, e.g., between about 50 and 150 vol. solvent/100 vol. crude oil, and solvent extraction temperatures above 100 F. are employed. Further, in respect to the naphthenic residual stocks and distillates, a low yield of refined oil results from the high solvent power of N- methyl-2-pyrrolidone.

Hereinbefore and hereinafter, the term essentially anhydrous means a water content of zero to less than about 1 wt. percent.

SUMMARY OF THE INVENTION In accordance with this invention, finished naphthenic lubricating oils are produced from naphthenic base crude oil by vacuum distillation, solvent refining of the vacuum distillate or residual stock with aqueous N-methyl-Z-pyrrolidone as a selective solvent and optionally inhibitor addition. We have unexpectedly discovered in the solvent refining step, by incorporating between about 2 and 15 wt. percent water basis total solvent in the N-methyl-Z- pyrrolidone, undesirable miscibility, increased viscosity and low refined oil yield are avoided.

DETAILED DESCRIPTION OF THE INVENTION Specifically, in the solvent refining step, the vacuum naphthenic distillate or residual naphthenic lubricating oil stock is contacted with N-methyl-Z-pyrrolidone having a water content of between about 2 and 15 wt. percent, preferably between about 3 and 10 wt. percent, at a temperature of at least 50 F. and below the temperature of complete miscibility of said naphthenic lubricating oil stock in N-methyl-2-pyrrolidone and at a dosage effective to dissolve at least 10 volume percent of said lubricating oil stock. The foregoing solvent extraction step produces a refined lubricating oil stock of improved viscosity index, improved thermal stability and improved oxidation stability. The manufacture of a merchantable naphthene base lubricating oil does not require dewaxing and only the addition of usual inhibitors is necessary.

Specific examples of naphthenic oil contemplated herein are oils used in the manufacture of turbine lubricating oils of an SUS viscosity at 100 F. of between about 100 and 600; refrigeration oils of an SUS viscosity at 100 F. of between and 600; and cylinder oils of an SUS viscosity at F. of between 1000 and 4000. Typically, the viscosity index of naphthenic base lubricanting oil charge stocks is within the range of about -10 to 50 and the viscosity index of the refined lubricating oil stock is at least 10 units higher.

The extraction temperatures and dosages in refining naphthene oils are advantageously within the range of 50 to 200 F., preferably within the range of 75 to F. and 30 to 300%, and preferably 75 to 200% respective y.

A typical processing sequence which may be used in the manufacture of lubricating oils in accordance with the process of this invention is crude naphthenic oil is passed to crude distillation facility. In the crude distillation facility the crude oil is separated into lower boiling fractions, forexample gas and fuel distillates and gas oils, mediumboiling fraction such as naphthenic lubricating oil distillates and crude residuum. The lubricating oil naphthenic distillate and/or naphthenic residual lube stock is passed to aqueous N-methyl-Z-pyrrolidone solvent extraction 4 using N-methyl-Z-pyrrolidone having varying water contents. The conditions and results are set forth below in Tables II, HA and Table 11B:

facility wherein the lubricating oil distillate and/or stock 5 TABLE 11 is contacted with aqueous N-methyl-Z-pyrrolidone result- Unw Run ing in separation of an extract comprising solvent and fined solvent soluble materials and raflinate comprising solvent Cmldmmls marge G H I refined lubricating oil. The extract and raflinate are sep- Solvegt composition, wei ht perarated and the lube oil raifinate is optionally combined can N-methyl-Z- olidone 100 100 98 with standard corrosion and/or oxidation inhibitors as s lwat 'gir 08 3 5 0 vent osage v0 ume percen 1 3X yvell as the standard detergent dlspersants requlred) Extractiontengpemtmlw no no 1m in a subsequent lube 011 product blend. Raflinate tests:

Standard apparatus and distillation, blending and sepaffifififi 441 411 275 ration techniques are applicable to the subject method. 0F 50.4 50.9 47.6 50.9

A viscositg i 1 49 sg 1 4860 1 4732 1 1 4833 E MPLE I Yield, voiuaa'ti at 66.6 39.6 66.6

This example demonstrates the method of the inven. Extract tests; RI at 70 C 1-5234 1-5162 1-5465 tion and the criticality of using water to modify the solvent power of N-methyl-Z-pyrrolidone' to permit control TABLE HA of refined oil quality and yield.

In a specific application of this invention, a residual 352% Run naphthenic lubricating oil stock is separated from crude Conditions charge I K L 011 byvacuum distillation. The naphthen c 011 stock is solvent compositionweight extracted in a l2-stage countercurrent mixer-settler expellizcentrth 1% nd 98 95 95 traction apparatus using N-methyl-Z-pyrrolidone having it};zjfi ff ff ijjjjjj "j 2 5 5 varying water contents. The conditions and results are go t o agavohz e gegeentu 3Xllllg tog 3x103 6et forth below in Tables I and 1A: g t g 1 1 11 Viscosi SUS at: TABLE I 3s 3 .3 3 .3 3 3111:; Run vlscosi'itoyo gii n 1 iii? 1 47 32 fidid 1 47% Cmldmms charge A B 0 Yield, voiufii'ei '65. '97s '55. 0 solvent composition, weight percent: Extract tests; RI at 70 0-- 1. 5382 1 5977 1.5255

N-methyl-Z-pyrrolidone 100 100 100 Water 0 0 0 35 golgentidosiage, volltime gerFcenL 15g fig I 1'80 011 6111 a life R Vi t 1 TABLE IIB sees 57, a Unre- Run 8 diti fined M N g 1 12553 316 1 200 Con ons charge oor n Solvent com sition,wei ht ercent:

RI at 70 0 1.5105 1.4719 Nmth i e mndoilef 9o 90 Yield, volume percent 36 w t 10 10 Extract es Solvent dosage, volume percent. 100 3X100 V c y. BUS a Extraction temperature, 11-.. 110 110 5x1?" x ri i eus t RI at 70 (:IIIIIIIIII 1. 5319 1. 5455 1.5229 io ti ii 441 High viscosity of extraction mix- 210 F ture Yes Yes Yes Yes viscosity Index 0 R1 at 70 Yield, volume percent 97. 4 90. 8 TABLE IA Extract tests; RI at 70 C 1.5537 1. 5677 Unre- Run fined Conditions charge D E F EXAMPLE III solvent 00m 1011, Weight W This example illustrates the advantage of water over N-m th -2- lid 00 5 90 Watei' f? 1 0 10 aldehydes, ketones, glycols, sulfolane and orgamc aclds solvent 8 volume P 98 150 as a solvent modifier for N-methyl-Z-pyrrolidone refining E titi t so 0 180 nimifatg ieiti 1 18 of naphthemc lubrlcatmg 011s. The conditions and results iwosityfisvs at 3 895 2 020 2 020 are set forth below in Tables III and IIIA. These data IZZ: "I show that water will more efiectively reduce the solvent Viscosity Index 70 70 color Lofibond W 1,200 760 760 power of N methyl 2 pyrrohdone than w1ll the other R1 at 70 0 1.5105 1. 4733 1. 4876 1. 4875 P E ili t lg nr oliime percent 4.3 69 74 viscosigyi SUS at: TABLE m 100 Unre- Run iii $76 25 fined a High viscosity of extraction mix Conditions charge 0 P Q tum Solve'nt compostion, weight percen 2 N-meth l-2- yrrolidone. 100 95 95 EXAMPLE II waterniuf. 0 2 Benzaldehyde- This example demonstrates the method of the mven- %olve i dosae volume 0 3x100 3x100 3x100 tron and the advantage of maintaining the solvent water gg fif g tg gi 11 content between about 2 and 10 wt. percent for refining RI at 70 C 1.4985 1. 4708 1.4775 1. 4723 naphthenic distillate. s gg gggw 6M a specific application of this invention, a distillate 3132? 441 275 326 291 naphthemc lubricating oil stock is separated from crude viscosity f 'dgi: 2% 5? 32 4-} oil b vacuum distillation. The na hthenic oil stock is Pour F -20 -20 -20 -20 y p Extract tests; RI at 70 0 1.5152 1 5322 1,5177

extracted in a single stage batch extraction operation The carge and product test data are given below in Table IV:

6 is required to make the same viscosity index raflinate (refined oil) with aqueous N-methyl-Z-pyrrolidone than with anhydrous furfural. Additionally, a higher yield of TABLE 111.4 R refined o1l 1s obtained 'Wllh aqueous N-methyl-Z-pyrroh- 2 ,133; done at the same viscosity index level. The test data and Condi ions charge .R s T U results are reported below in Table V:

Solvent composition, weight TABLE V percent:

N -methyl-2-pyrrolidone 95 95 95 95 Unre- Run Sulfolane 5 fined griettihylere glycol. 5 "5 Conditions charge W X Diisobutyl ketone. Solvent Furfural Solvent dosage 3x100 3x100 3x100 8Xl00 Water content, weight percent 0 5. 0 lrltgiactmi tetmperature, F 110 110 110 110 golgrent dostoge, volume percent. 150 98 na e es s: 1: rec ion empera ure. 155 180 RI at 70 C 1.4985 1.473 1.4748 1.474 1.4730 Rafiinate tests:

Yield, volume percent 46. 5 51. 8 51. 8 36. 1 Viscosity, SUS at:

Viscosity see at: 100 F 2 020 2 020 Viscosity index- 0 45 41 41 56 10 10 Pour, F 20 20 -20 20 300 750 Extract tests, RI at 70 C 1. 5206 1. 5240 1.5296 1. 5129 1. 4875 1. 4876 2 EXAMPLE IV 0 N-methyl-Z-pyrrolidone. This example illustrates the method of the invention EXAMPLE VI and shows that the refined oils exhibit superior color, Thisexamplemustrates t he unexpected aspects of the g3: 2:32: x i gzg xi g gg figgggz 2%? character invention; by a comparison of solvent refining of residual A f P t d b di tin ti f h naphthenic and paraflimc lube 011s under comparable ractlon P 6 y vacfmm S a on o conditios in a multistage countercurrent mixer-settler thenrc crude oil 15 treated w1th N-methyl-Z-pyrrohdone apparatus That is the quality and yield of paraffirlic oil g t fii' extracnon P can be controlled whereas that of the naphthenic oil canra us un er e O owmg con Ions not, unless water is added to N-methyl-2-pyrrolidone. Processing conditions 9 The unrefined oil fractions employed were as follows:

Solvent dosage, vol. percent 147 Unw Unw Solvent water content, Wt. percent 2.6 fined fined, Extraction temperature, F. 110 y i 5 12 Refined oil yield, vol. percent 74.5 Tests oil 011 The charge and product test data are glven below 1n Viscosity, SUS at: Table IV: 3, egg 3, s9;

1 14 TABLE IV.--CHARGE AND PRODUCT TESTS Viscosity index 77 4s Pour, +12 10 Ume Refingg 1.4959 1. 5105 fined rai charge finate Extract The solvent extraction process conditions employed Gravity,APl'. s 21.2 25.2 93 are as follows: Flash, 000, F 390 420 330 Viscosity SUS at: R

00: F 324 246 1, 052 P053215: 45 Paratfinic Naphthenic Ash, weight percen None Carbonhresidue, weight percent 0. 02 Oil AA BB CC DD EE 1 P number s l nt Fu 1 MP 2 Fu 1 p 9 p 2 Solvent dosage, volume percent. 172 150 98 sulfur, e: w 50 exes???992221223? 0 0 o 5 0 ig ggffii i j 40/1/2 /6 Extraction temperature, F-... 210 170 155 180 135 After 24 hrs. at 220 F. 50/1/2 /6 1 Fu=FurfuIa1 Color stability at 400 F., Llvibond:

Inhitial, or 6 Ben-n 128?;2 328% u 2 MP N methyl 2pyrrolldone.

1 our 1 RI 2thog1r" Hog g 454%2 HU 55 The results are reported below in Table VT:

SOD. lead corrosion 325 F.;! weight TABLE VI oss m in. at:

1 E 5, 4 0,3 Raflinate tests AA BB 00 DD EE 6 hours 21. 7 2. 1

Heat Test, 125 hours at 400 Gravity 8 9 2 6 22. 6 Evaporation loss, percent 16. 7 11. 9 viscosigyr SUS at:

Viscosity increase cs. at 210 F., per-.- 60 2,200 2,020 2,020 1.186

Viscosity index- 93 92 86 Pour, 120 15 1 The S.0.D. Lead Corrosion Test is a bench test of corrosion resistance Yield Volume Percent 75 49 which is described in Military Specification MILL- 708C, Lubricating Oil, Aircraft Turbine Oil, Synthetic Base, dated November 2, 1955 and is described in detail in U.S. Patent 3,003,963.

2 The Heat Test is a bench test for thermal stability in which a 250 milliliter sample of the oil under test is heated for hours at 250 F. and then held at room temperature for 1 day. The sample is then weighed to determine the evaporation loss, the viscosity is determined and compared with the oil before heating, the neutralization number is determined and the presence or absence of sludge is noted.

EXAMPLE V This example illustrates the advantages of aqueous N-methyl-Z-pyrrolidone over anhydrous furfural refining of naphthenic lubricating oil.

The example shows that a much lower solvent dosage EXAMPLE VI I cosity index of lubricating oil stocks at the same condi- TABLE vm tions of temperature and dosage. A greater reduction in the refractive index of the refined oil is obtained with s N-methyl-Z-pyrrolidone and the reduction in refractive Conditions charge LL MM index in treating the high viscosity lubricating oil stock solventoomposmonyweightpercent: with N-methyl-2-pyrrolidone is greater than in treating aurfnml 100 95 the intermediate viscosity lubricating oil stock. The results solvegggsagey weight percent g 3 are shown in Table VII and VIIA: p rat 150 150 Ratfinate tests: TABLE VII ViSGiJSgyFSUS at:

a 9 Residual stock 210 i4; ii f i Viscosity inde 48 70 70 Unre- R1111 R]: at 70 C... 1, 5105 1, 4907 1. 4897 fined Yield, volume percent. 75. 5 75. 7 Conditions charge FF GG HH II Extract tests; RI at 70 C 5714 0 Solvent com sition Wei ht percent: p0 g We claim:

55%?i552ifffiiiiiiiJ1i:1131---??? "ta'... ."f ""e:a In the Solvent refining of a naphthenic lubricating Water 5.0 5. 0 2. 5 2. 5 011 charge stock of a Viscosity index of b t bo .10 flgf ff fffffii ff ffjff' 200 200 200 200 nd 50 for the removal of constituents havinga low vis- Temperature 150 150 150 150 coslty index, poor thermal stability and poor oxidation Rafiivlilictgs i sg g us at: stability, the improvement which comprises contacting said 100: F...--------.. 3,895 2,078 2, 846 2,170 3,035 lubricating oil stock with a wet solvent consisting essen- ViSCQQWih-diIH :3 1 3 tially of between about 2 and 15 wt. percent water and 1;; {it 10 0 11-- 1. 5105 1. 13 1. 1; 1. 392; 1. 431: between about 85 and 98% .N-methyl-Z-pyrrolidone at a sliriaties'esz'izi;r'aa ='e'::::::::::1.5354 1.5750 1 5642 1. 61 71 temperature 9 E p g e temperature of complete mlscibillty of said lubricat ng 011 stock in said TABLE VHA wet solvent and at a dosage effective to dissolve at least 10 volume percent of said lubricating oil stock whereby Distillate Stock a refined lubricating oil stock is produced of a viscosity Run index at least 10 units higher than the lubricating oil fined charge stock, and of improved thermal stability and imcmlditmns charge H KK proved oxidation stability. solv e ntgegu eg ygg p 97 5 2. The process of claim 1 wherein the solvent dosage argmiiann 1 97 5 is within the range of 30 and @00 volume percent, and the WaWf- 5 contacting temperature is within the range of 50 to 200 (F. Solvent dosage, volume percent 200 200 3 5 Temperature 150 150 Raffinate tests: References Cited 00 441 358 442 UNITED STATES PATENTS 210 50.4 49.6 50.9 vl scosi tsg i ld 1 2 1 2g 8 2,767,119 10/ 1956 FOI'ChlClll 196-23 i* ,3 1; 2,133,691 10/1'938 Fran is 1 13 Extract tests: RI at 70 C l. 5255 1. 5719 DELBERT E. GANTZ, Primary Examiner EXAMPLE VIII I. M. NELSON, Assistant Examiner This example shows that addition of 5 wt. percent water to furfural has no effect on the quality or yield of a refined US. Cl. X.R.

naphthenic residual oil, and the solvent dosage for hydrous furfural is twice that of anhydrous cfurfural. The batch extraction on results are shown in Table VIII. 

